The JCMT Gould Belt Survey: A First Look at Dense Cores in Orion B

Abstract

We present a first look at the SCUBA-2 observations of three sub-regions of the Orion B molecular cloud: LDN 1622, NGC 2023/2024, and NGC 2068/2071, from the JCMT Gould Belt Legacy Survey. We identify 29, 564, and 322 dense cores in L1622, NGC 2023/2024, and NGC 2068/2071 respectively, using the SCUBA-2 850 µm map, and present their basic properties, including their peak fluxes, total fluxes, and sizes, and an estimate of the corresponding 450 µm peak fluxes and total fluxes, using the FellWalker source extraction algorithm. Assuming a constant temperature of 20 K, the starless dense cores have a mass function similar to that found in previous dense core analyses, with a Salpeterlike slope at the high-mass end. The majority of cores appear stable to gravitational collapse when considering only thermal pressure; indeed, most of the cores which have masses above the thermal Jeans mass are already associated with at least one protostar. At higher cloud column densities, above 1 − 2 × 10 23 cm −2 , most of the mass is found within dense cores, while at lower cloud column densities, below 1 × 10 23 cm −2 , this fraction drops to 10% or lower. Overall, the fraction of dense cores associated with a protostar is quite small (< 8%), but becomes larger for the densest and most centrally concentrated cores. NGC 2023/2024 and NGC 2068/2071 appear to be on the path to forming a significant number of stars in the future, while L1622 has little additional mass in dense cores to form many new stars.

The JCMT Gould Belt Survey: A First Look at SCUBA-2 Observations of the Lupus I Molecular Cloud

“…Compared to other regions observed with SCUBA-2, e.g. Ophiuchus (Pattle et al 2015), Orion A (Salji et al 2015;Mairs et al 2016), Orion B (Kirk et al 2016) and Perseus (Chen et al 2016), the maps show much less evidence of bright, compact objects and clustered structures. Its appearance is more in line with the relatively quiescent Auriga-California Nebula (BroekhovenFiene et al, in preparation), although even Auriga-California contains more structure than Lupus I.…”

“…For a separate core to be identified, it must contain emission at a minimum specified value that can act as the peak. The FellWalker algorithm has been used previously by Rumble et al (2015) for the identification and characterization of cores in the Serpens MWC 297 region, and Kirk et al (2016) …”

On the spatial distributions of dense cores in Orion B

“…We quantify the spatial distributions of dense cores in three subregions of the Orion B star-forming region, namely L1622, NGC 2068/NGC 2071, and NGC 2023/NGC 2024, using data from Kirk et al (2016a). We determine the amount of substructure using the Cartwright & Whitworth (2004) Q-parameter, the amount of mass segregation using the Allison et al (2009) MSR ratio, the relative surface density of the most massive cores using the Maschberger & Clarke (2011) LDR technique, and the relative depth of the gravitational potential around the most massive cores, PDR (Parker & Dale 2017).…”

Alma Resolves the Torus of NGC 1068: Continuum and Molecular Line Emission

“…The opacity of the dust is quite uncertain and a source of significant on-going research. Following the GBS standard (Pattle et al 2015;Rumble et al 2015Rumble et al , 2016Salji et al 2015aSalji et al , 2015bKirk et al 2016aKirk et al , 2016bLane et al 2016;Mairs et al 2016), we adopt k = 0.0125 850 cm 2 g −1 . Taking a fiducial value for the temperature from Appendix A,…”